Irrigation—Principles & PracticesUnit 1.5 | Part 1 – 241Variety Selection
In any dry farming system, variety selection is absolutely
critical. Varieties that do well as dry-farmed crops typi-
cally have an aggressive root system capable of reaching
deep into the soil horizon to tap the stored rain moisture.
It is interesting to note that growers in the Central
Coast region have trialed literally hundreds of varieties of
heirloom, open pollinated and hybrid tomatoes and, to
date, none have compared to ‘Early Girl’ in their ability
to set roots deep and consistently produce a high yield
of high quality, flavorful, and marketable fruits with no
irrigation. ‘New Girl’, a recently introduced variety, is
closely related to ‘Early Girl’ and appears to have many of
the same favorable characteristics.
Plant Spacing and Weed Control
Dry-farmed crops with extensive root systems
can effectively extract deep residual rain mois-
ture from a fairly large area within their roots’
grasp. Competition from other nearby crop
plants or weeds can result in water-stressed
plants that produce very little fruit and remain
stunted. For this reason it is critical to plant
out dry-farmed crops in a much wider spac-
ing than is typically used for irrigated crops
of the same type. Good weed management in
a dry farm system is also critical, since most
weeds have aggressive root systems capable of
outcompeting most crop plants for both water
and nutrients.
As an example of plant spacing, irrigated
tomatoes are commonly spaced 2 feet apart
within the row with rows spaced 4 feet apart,
a density of roughly 5,400 plants per acre.
A typical spacing for dry-farmed tomatoes
(depending on soil type and rainfall amounts)
would be 6 feet between rows and 6 feet
between plants, for a total plant population of
1210 plants per acre. As you can see from this
example a significant yield reduction can be
expected from most dry-farmed crops simply
based on per acre plant populations. A higher
price premium for dry-farmed tomatoes will
often make up for the yield loss related to
wider spacing.Crops Suitable for Dry Farming
Tomatoes are the most notable dry-farmed
crop produced in the Central Coast region.
Dry-farmed tomatoes are typically transplant-
ed into the field from May through June. It is
advantageous to plant the tomatoes as deep as
possible into the residual rain moisture after
the dust mulch has been created and when soil
temperatures are adequate for strong growth
(>55 ºF). Growers often plant several succes-
sions spaced 2 to 3 weeks apart to provide an
extended fall harvest period. Some growers
stake and tie the tomatoes for ease of harvest
and to enhance fruit quality, while others let
the plants vine out on the ground without
support.The typical springtime dry farm tillage and crop culture
sequence at the UCSC Farm is as follows:
Flail mow cover crop
Incorporate cover crop residue with mechanical spader
Form beds with rolling cultivator
In the absence of rain, pre-irrigate beds with over head
irrigation at a rate of 1.5 inches per acre (when spring
rains are adequate this step is unnecessary)
Wait for weed flush and create dust mulch with rolling
cultivator
Maintain dust mulch with rolling cultivator as needed
until planting time
At time of planting break open bed middles with
Alabama shovels and plant tomato transplants deeply
into moisture using hand trowels
Cultivate with sweeps and side knives when first weeds
appear in furrow bottoms or as necessary to maintain
dust mulch
Once plants reach adequate height, reform beds by
throwing dirt into bed middles with rolling cultivator
—when timed well this last cultivation pass will also
effectively smother weeds starting to establish within
the plant line1
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4456789Supplement 4: Overview of Dry Farming